U.S. patent application number 15/403551 was filed with the patent office on 2017-08-24 for chopper device.
This patent application is currently assigned to Fuji Electric Co., Ltd.. The applicant listed for this patent is Fuji Electric Co., Ltd.. Invention is credited to Motoyoshi KUBOUCHI, Ryohei MAKINO.
Application Number | 20170244319 15/403551 |
Document ID | / |
Family ID | 59631238 |
Filed Date | 2017-08-24 |
United States Patent
Application |
20170244319 |
Kind Code |
A1 |
MAKINO; Ryohei ; et
al. |
August 24, 2017 |
CHOPPER DEVICE
Abstract
A chopper device includes: a series circuit connecting at one
end to a positive pole of a DC power source and having a breaker
and a reactor; a series circuit connected between another end of
the stated series circuit and a negative pole of the DC power
source and having switches; a series circuit connected in parallel
to the switch and having a diode and a capacitor; and a series
circuit connected in parallel to the switch and having a diode and
a capacitor. The chopper device outputs a DC voltage at three
potentials from both ends and a midpoint of a series circuit having
the capacitors by turning the switches ON/OFF. The chopper device
further includes other switches connected in parallel to the
switches. When a short-circuit fault is presumed to have occurred
in the switch, the other switch is turned ON before interruption is
performed by the breaker.
Inventors: |
MAKINO; Ryohei; (Tokyo,
JP) ; KUBOUCHI; Motoyoshi; (Nagano, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fuji Electric Co., Ltd. |
Kanagawa |
|
JP |
|
|
Assignee: |
Fuji Electric Co., Ltd.
Kanagawa
JP
|
Family ID: |
59631238 |
Appl. No.: |
15/403551 |
Filed: |
January 11, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 1/32 20130101; H02M
3/135 20130101; H02M 7/483 20130101; H02P 27/06 20130101; H02P
29/0241 20160201; H02H 7/1225 20130101 |
International
Class: |
H02M 3/135 20060101
H02M003/135; H02P 27/06 20060101 H02P027/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 22, 2016 |
JP |
2016-030742 |
Claims
1. A chopper device, comprising: a DC power source; a series
circuit having a breaker and a reactor connected in series, one end
of the series circuit being connected to one pole of said DC power
source; a switch series circuit having a first switch and a second
switch connected in series, said switch series circuit being
connected between another end of said series circuit and another
pole of said DC power source; a first series circuit having a first
diode and a first capacitor connected in series, said first series
circuit being connected in parallel to said first switch; and a
second series circuit having a second diode and a second capacitor
connected in series, said second series circuit being connected in
parallel to said second switch, wherein said first capacitor and
said second capacitor are connected in series, defining a capacitor
series circuit, wherein said first switch and said second switch
are turned ON and OFF to output DC voltages at three potentials
from both ends and a midpoint of said capacitor series circuit
having said first capacitor and said second capacitor, thereby
supplying the DC voltages to a load, wherein the chopper device
further includes a third switch connected in parallel to said first
switch and a fourth switch connected in parallel to said second
switch, and wherein when a short-circuit fault is detected to have
occurred in said first switch, said fourth switch is turned ON
before interruption is performed by said breaker, and when a
short-circuit fault is detected to have occurred in said second
switch, said third switch is turned ON before interruption is
performed by said breaker.
2. A chopper device, comprising: a DC power source; a series
circuit having a breaker and a reactor connected in series, one end
of the series circuit being connected to one pole of said DC power
source; a switch series circuit having a first switch and a second
switch connected in series, said switch series circuit being
connected between another end of said series circuit and another
pole of said DC power source; a first series circuit having a first
diode and a first capacitor connected in series, said first series
circuit being connected in parallel to said first switch; and a
second series circuit having a second diode and a second capacitor
connected in series, said second series circuit being connected in
parallel to said second switch, wherein said first capacitor and
said second capacitor are connected in series, defining a capacitor
series circuit, wherein said first switch and said second switch
are turned ON and OFF to output DC voltages at three potentials
from both ends and a midpoint of said capacitor series circuit
having said first capacitor and said second capacitor, thereby
supplying the DC voltages to a load, wherein the chopper device
further includes a third switch connected in parallel to said first
capacitor and a fourth switch connected in parallel to said second
capacitor, and wherein when a short-circuit fault is detected to
have occurred in said first switch, said fourth switch is turned ON
before interruption is performed by said breaker, and when a
short-circuit fault is detected to have occurred in said second
switch, said third switch is turned ON before interruption is
performed by said breaker.
3. A chopper device, comprising: a DC power source; a series
circuit having a breaker and a reactor connected in series, one end
of the series circuit being connected to one pole of said DC power
source; a switch series circuit having a first switch and a second
switch connected in series, said switch series circuit being
connected between another end of said series circuit and another
pole of said DC power source; a first series circuit having a first
diode and a first capacitor connected in series, said first series
circuit being connected in parallel to said first switch; and a
second series circuit having a second diode and a second capacitor
connected in series, said second series circuit being connected in
parallel to said second switch, wherein said first capacitor and
said second capacitor are connected in series, defining a capacitor
series circuit, wherein said first switch and said second switch
are turned ON and OFF to output DC voltages at three potentials
from both ends and a midpoint of said capacitor series circuit
having said first capacitor and said second capacitor, thereby
supplying the DC voltages to a load, wherein the chopper device
further includes a third switch connected in parallel to said
switch series circuit, wherein when a short-circuit fault is
detected to have occurred in said first switch or said second
switch, said third switch is turned ON before interruption is
performed by said breaker.
4. A chopper device, comprising: a DC power source; a first series
circuit having a breaker and a reactor connected in series, one end
of said first series circuit being connected to one pole of said DC
power source; a first switch connected between another end of said
first series circuit and another pole of said DC power source; and
a second series circuit having a diode and a capacitor connected in
series, said second series circuit being connected in parallel to
said first switch, said first switch being turned ON and OFF to
output a DC voltage at a prescribed magnitude from both ends of
said capacitor, wherein the chopper device further includes a
second switch connected in parallel to said first switch, and
wherein when a state of overvoltage is detected to have occurred in
said capacitor, said second switch is turned ON before interruption
is performed by said breaker.
5. A chopper device, comprising: a DC power source; a first series
circuit having a breaker and a reactor connected in series, one end
of said first series circuit being connected to one pole of said DC
power source; a first switch connected between another end of said
first series circuit and another pole of said DC power source; and
a second series circuit having a diode and a capacitor connected in
series, said second series circuit being connected in parallel to
said first switch, said first switch being turned ON and OFF to
output a DC voltage at a prescribed magnitude from both ends of
said capacitor, wherein the chopper device further includes a
second switch connected in parallel to said capacitor, and wherein
when a state of overvoltage is detected to have occurred in said
capacitor, said second switch is turned ON before interruption is
performed by said breaker.
6. The chopper device according to claim 1, wherein said third
switch and said fourth switch are housed in a different package
from said first switch or said second switch.
7. The chopper device according to claim 2, wherein said third
switch and said fourth switch are housed in a different package
from said first switch or said second switch.
8. The chopper device according to claim 3, wherein said third
switch is housed in a different package from said first switch or
said second switch.
9. The chopper device according to claim 1, wherein said first
diode and said first switch are housed in the same package, and
said second diode and said second switch are housed together in a
different package.
10. The chopper device according to claim 1, wherein said third
switch and said fourth switch are housed in the same package.
11. The chopper device according to claim 2, wherein said third
switch and said fourth switch are housed in the same package.
12. The chopper device according to claim 1, wherein said third
switch and said fourth switch are housed in mutually different
packages.
13. The chopper device according to claim 2, wherein said third
switch and said fourth switch are housed in mutually different
packages.
14. The chopper device according to claim 1, wherein said first
diode and said third switch are housed in the same package, and
said second diode and said fourth switch are housed together in a
different package.
15. The chopper device according to claim 2, wherein said first
diode and said third switch are housed in the same package, and
said second diode and said fourth switch are housed together in a
different package.
16. The chopper device according to claim 4, wherein said diode and
said first switch are housed in the same package.
17. The chopper device according to claim 4, wherein said diode and
said first switch are housed in the same package.
18. The chopper device according to claim 1, wherein elements
constituted by wide band-gap semiconductors are used as said first
switch and said second switch, and an element constituted by a
silicon semiconductor is used as said third switch or said fourth
switch.
19. The chopper device according to claim 4, wherein an element
constituted by a wide band-gap semiconductor is used as said first
switch, and an element constituted by a silicon semiconductor is
used as said second switch.
20. The chopper device according to claim 1, wherein an element
constituted by a wide band-gap semiconductor is used as said diode.
Description
BACKGROUND OF THE INVENTION
[0001] Technical Field
[0002] This invention relates to a chopper device, used in a field
such as railways, that transforms an input DC voltage into a DC
voltage of a predetermined magnitude and outputs the resulting DC
voltage.
[0003] Background Art
[0004] FIG. 31 is a circuit diagram illustrating an example of a
conventional three-level chopper device.
[0005] In FIG. 31, a breaker 2 constituted by a current
interrupting device having a mechanical contact, a fuse, or the
like, a reactor 3, and semiconductor switching elements (also
simply called "switches" hereinafter) 4 and 5 are connected in
series between a positive pole and a negative pole of a DC power
source 1. Here, insulated gate bipolar transistors (IGBTs), MOS
field effect transistors (MOSFETs), bipolar power transistors, or
the like are used for the switches 4 and 5.
[0006] A diode 6 and a capacitor 8 are connected in series to
respective ends of the switch 4, and a diode 7 and a capacitor 9
are connected in series to respective ends of the switch 5.
[0007] Both ends of a series circuit constituted by the capacitors
8 and 9 and a connection point (midpoint) between the capacitors 8
and 9 serve as output terminals of the chopper device. A load 101,
including a half-bridge inverter constituted by switches 10 and 11
such as IGBTs and an AC motor 12, is connected between the output
terminals.
[0008] According to this chopper device, energy stored in the
reactor 3 is supplied to the series circuit constituted by the
capacitors 8 and 9 by the switches 4 and 5 turning on and off, and
a DC voltage at three potentials is outputted to the load 101 from
the series circuit. Here, the voltages of the capacitors 8 and 9
are controlled to higher values than the voltage of the DC power
source 1, and thus the circuit illustrated in FIG. 31 functions as
a three-level boosting chopper device.
[0009] Note that the load 101 operates so as to transform the DC
voltage into an AC voltage by the switches 10 and 11 of the
half-bridge inverter turning on and off and supply the AC voltage
to the motor 12.
[0010] When a fault occurs in such a chopper device, protective
measures are typically taken by turning the switches 10 and 11 of
the inverter off and separating the load 101 from the chopper
device, and furthermore turning the switches 4 and 5 that implement
chopper operations off so that current does not flow in the load
101.
[0011] However, when a short-circuit fault where, for example, the
one switch 4 in the chopper device is fully conductive occurs, the
equivalent circuit illustrated in FIG. 32 is formed. Normal
measures in this case are turning the switches 10 and 11 off,
separating the load 101, and turning the other switch 5 in the
chopper device off.
[0012] FIG. 33 illustrates an equivalent circuit in the case where
the load 101 has been separated and the switch 5 has been turned
off in response to a short-circuit fault in the switch 4.
[0013] In this circuit, series resonance current produced by the
reactor 3 and the capacitor 9 flows from the DC power source 1 via
the short-circuited switch 4, along a path a indicated by the
broken line. Because the switch 4 is short-circuited, the series
resonance current cannot be controlled. There is thus a risk that
the capacitor 9 will be charged to a higher voltage than the
voltage of the DC power source 1 (that is, to a voltage greater
than the breakdown voltage of the capacitor 9). Particularly, with
this type of chopper device, although there are cases where the
device operates with the voltage of the capacitor 9 at a lower
value than the voltage of the DC power source 1 during normal
operations, the voltage of the capacitor 9 may rise to
approximately three times the voltage occurring in normal
operations when series resonance current flows along the path a
indicated in FIG. 33.
[0014] Meanwhile, in the case where the chopper device is installed
in a rail car, the voltage of the DC power source 1 supplied from a
contact wire fluctuates frequently due to pantograph bounce,
regenerative driving of other cars, and so on. Particularly, if a
DC source voltage fluctuates drastically, there is a risk that the
capacitor 9 will reach an even higher voltage due to the series
resonance current in the path a. Assuming an electrostatic
capacitance of the capacitor is represented by C and the voltage by
V, generally, when a voltage that greatly exceeds the breakdown
voltage is instantaneously applied to the capacitor, energy
equivalent to CV.sup.2/2 is released all at once, which causes the
capacitor to explode.
[0015] Opening the breaker 2 can be thought of as a method for
interrupting the series resonance current in the path a illustrated
in FIG. 33. However, in the case where the breaker 2 is constituted
by a fuse, for example, the fuse can only be melted by a large
current and it takes a certain amount of time for the fuse to be
completely melted. There is thus a risk that the voltage in the
capacitor 9 will rise before the fuse melts. It is thus desirable
that the series resonance current be interrupted by the breaker 2
before the voltage of the capacitor 9 rises. However, in the case
where the inductance of the reactor 3 is high, a large surge
voltage may arise if current flowing in the reactor 3 is forcefully
interrupted by the breaker 2, which may damage the switches and the
like. The melting time for the fuse must therefore be somewhat
long.
[0016] Even if the breaker 2 is constituted by a current
interrupting device having a mechanical contact, there is a time
delay in the operation of the contact, and thus the operation may
be too late for the rise in the voltage of the capacitor 9.
[0017] Thus as described above, it is difficult to completely
prevent the capacitor 9 from being damaged by overvoltage by
interrupting the series resonance current using the breaker 2.
[0018] Note that Patent Document 1 discloses related art in which,
in a chopper device having substantially the same configuration as
that illustrated in FIG. 31, a short-circuit fault or the like is
detected in the capacitor on the basis of a potential at a midpoint
in the capacitor series circuit, and operations of the switches in
the chopper device are then limited.
RELATED ART DOCUMENT
Patent Document
[0019] Patent Document 1: Japanese Patent Application Laid-Open
Publication No. 2008-236863 (paragraphs [0079] to [0081], FIG. 1,
and so on)
SUMMARY OF THE INVENTION
[0020] As described above, in the case where a short-circuit fault
has occurred in a switch in a chopper device, there has thus far
not been a useful technique for protecting a capacitor on the
output side from being damaged by overvoltage. Such a technique is
therefore needed.
[0021] As such, a problem to be solved by the present invention is
to provide a chopper device capable of reliably preventing an
output-side capacitor from being damaged by overvoltage even in the
case where a fault has occurred in a switch, and furthermore
capable of ensuring minimal necessary replacement of faulted
semiconductor elements as economically as possible. Accordingly,
the present invention is directed to a scheme that substantially
obviates one or more of the problems due to limitations and
disadvantages of the related art.
[0022] Additional or separate features and advantages of the
invention will be set forth in the descriptions that follow and in
part will be apparent from the description, or may be learned by
practice of the invention. The objectives and other advantages of
the invention will be realized and attained by the structure
particularly pointed out in the written description and claims
thereof as well as the appended drawings.
[0023] To achieve these and other advantages and in accordance with
the purpose of the present invention, as embodied and broadly
described, in a first aspect, the present disclosure provides a
chopper device, including:
[0024] a DC power source;
[0025] a series circuit having a breaker and a reactor connected in
series, one end of the series circuit being connected to one pole
of the DC power source;
[0026] a switch series circuit having a first switch and a second
switch connected in series, the switch series circuit being
connected between another end of the series circuit and another
pole of the DC power source;
[0027] a first series circuit having a first diode and a first
capacitor connected in series, the first series circuit being
connected in parallel to the first switch; and
[0028] a second series circuit having a second diode and a second
capacitor connected in series, the second series circuit being
connected in parallel to the second switch,
[0029] wherein the first capacitor and the second capacitor are
connected in series, defining a capacitor series circuit,
[0030] wherein the first switch and the second switch are turned ON
and OFF to output DC voltages at three potentials from both ends
and a midpoint of the capacitor series circuit having the first
capacitor and the second capacitor, thereby supplying the DC
voltages to a load,
[0031] wherein the chopper device further includes a third switch
connected in parallel to the first switch and a fourth switch
connected in parallel to the second switch, and
[0032] wherein when a short-circuit fault is detected to have
occurred in the first switch, the fourth switch is turned ON before
interruption is performed by the breaker, and when a short-circuit
fault is detected to have occurred in the second switch, the third
switch is turned ON before interruption is performed by the
breaker.
[0033] In a second aspect, the present disclosure provides a
chopper device, including:
[0034] a DC power source;
[0035] a series circuit having a breaker and a reactor connected in
series, one end of the series circuit being connected to one pole
of the DC power source;
[0036] a switch series circuit having a first switch and a second
switch connected in series, the switch series circuit being
connected between another end of the series circuit and another
pole of the DC power source;
[0037] a first series circuit having a first diode and a first
capacitor connected in series, the first series circuit being
connected in parallel to the first switch; and
[0038] a second series circuit having a second diode and a second
capacitor connected in series, the second series circuit being
connected in parallel to the second switch,
[0039] wherein the first capacitor and the second capacitor are
connected in series, defining a capacitor series circuit,
[0040] wherein the first switch and the second switch are turned ON
and OFF to output DC voltages at three potentials from both ends
and a midpoint of the capacitor series circuit having the first
capacitor and the second capacitor, thereby supplying the DC
voltages to a load,
[0041] wherein the chopper device further includes a third switch
connected in parallel to the first capacitor and a fourth switch
connected in parallel to the second capacitor, and
[0042] wherein when a short-circuit fault is detected to have
occurred in the first switch, the fourth switch is turned ON before
interruption is performed by the breaker, and when a short-circuit
fault is detected to have occurred in the second switch, the third
switch is turned ON before interruption is performed by the
breaker.
[0043] In a third aspect, the present disclosure provides a chopper
device, including:
[0044] a DC power source;
[0045] a series circuit having a breaker and a reactor connected in
series, one end of the series circuit being connected to one pole
of the DC power source;
[0046] a switch series circuit having a first switch and a second
switch connected in series, the switch series circuit being
connected between another end of the series circuit and another
pole of the DC power source;
[0047] a first series circuit having a first diode and a first
capacitor connected in series, the first series circuit being
connected in parallel to the first switch; and
[0048] a second series circuit having a second diode and a second
capacitor connected in series, the second series circuit being
connected in parallel to the second switch,
[0049] wherein the first capacitor and the second capacitor are
connected in series, defining a capacitor series circuit,
[0050] wherein the first switch and the second switch are turned ON
and OFF to output DC voltages at three potentials from both ends
and a midpoint of the capacitor series circuit having the first
capacitor and the second capacitor, thereby supplying the DC
voltages to a load,
[0051] wherein the chopper device further includes a third switch
connected in parallel to the switch series circuit,
[0052] wherein when a short-circuit fault is detected to have
occurred in the first switch or the second switch, the third switch
is turned ON before interruption is performed by the breaker.
[0053] In a fourth aspect, the present disclosure provides a
chopper device, including:
[0054] a DC power source;
[0055] a first series circuit having a breaker and a reactor
connected in series, one end of the first series circuit being
connected to one pole of the DC power source;
[0056] a first switch connected between another end of the first
series circuit and another pole of the DC power source; and
[0057] a second series circuit having a diode and a capacitor
connected in series, the second series circuit being connected in
parallel to the first switch, the first switch being turned ON and
OFF to output a DC voltage at a prescribed magnitude from both ends
of the capacitor,
[0058] wherein the chopper device further includes a second switch
connected in parallel to the first switch, and
[0059] wherein when a state of overvoltage is detected to have
occurred in the capacitor, the second switch is turned ON before
interruption is performed by the breaker.
[0060] In a fifth aspect, the present disclosure provides a chopper
device, including:
[0061] a DC power source;
[0062] a first series circuit having a breaker and a reactor
connected in series, one end of the first series circuit being
connected to one pole of the DC power source;
[0063] a first switch connected between another end of the first
series circuit and another pole of the DC power source; and
[0064] a second series circuit having a diode and a capacitor
connected in series, the second series circuit being connected in
parallel to the first switch, the first switch being turned ON and
OFF to output a DC voltage at a prescribed magnitude from both ends
of the capacitor,
[0065] wherein the chopper device further includes a second switch
connected in parallel to the capacitor, and
[0066] wherein when a state of overvoltage is detected to have
occurred in the capacitor, the second switch is turned ON before
interruption is performed by the breaker.
[0067] Note that in the sixth to twelfth aspects of the present
invention, the third switch and the fourth switch, or the third
switch alone, may be housed in a different package from a package
in which the first switch or the second switch is housed.
[0068] Additionally, the first diode and the first switch may be
housed in the same package, and the second diode and the second
switch may be housed together in a different package.
[0069] Alternatively, the third switch and the fourth switch may be
housed in the same package, or may be housed in mutually different
packages.
[0070] Furthermore, the first diode and the third switch may be
housed in the same package, and the second diode and the fourth
switch may be housed together in a different package.
[0071] Additionally, in the thirteenth to fifteenth aspects of the
present invention, it is desirable that elements constituted by
wide band-gap semiconductors be used as switches that perform
chopper operations, and that elements constituted by silicon
semiconductors be used as switches for protection.
[0072] Furthermore, it is desirable that elements constituted by
wide band-gap semiconductors be used as the diodes.
[0073] According to the first to fifth aspects of the present
invention, in the case where a short-circuit fault is presumed to
occur in a switch that performs chopper operations, or in the case
where there is an indication that an output-side capacitor will
enter a state of overvoltage, the capacitor can be prevented from
being damaged by the overvoltage by turning a switch for protection
on and eliminating a current path that passes through the
capacitor.
[0074] Additionally, packaging the diodes and switches in various
states as described in the sixth to twelfth aspects of the present
invention makes it possible to replace the minimum number of those
semiconductor elements on a package-by-package basis in the case
where those semiconductor elements have faulted and thus need to be
replaced.
[0075] In particular, using elements constituted by comparatively
high-cost wide band-gap semiconductors and elements constituted by
comparatively low-cost silicon semiconductors as the diodes and
switches depending on the situation, as described in the thirteenth
to fifteenth aspects of the present invention, makes it possible to
eliminate wasteful replacement of high-cost semiconductor elements
and improve the cost performance of the device.
[0076] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory, and are intended to provide further explanation of
the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0077] FIG. 1 is a circuit diagram illustrating Embodiment 1 of the
present invention.
[0078] FIG. 2 is an equivalent circuit diagram of the chopper
device illustrated in FIG. 1 in a case where one switch that
performs chopper operations has short-circuited.
[0079] FIG. 3 is an equivalent circuit diagram illustrating a case
where one protection switch has turned on in the state illustrated
in FIG. 2.
[0080] FIG. 4 is a circuit diagram illustrating Embodiment 2 of the
present invention.
[0081] FIG. 5 is a circuit diagram illustrating a comparison
example for comparison with Embodiment 2.
[0082] FIG. 6 is a circuit diagram illustrating a variation on
Embodiment 2.
[0083] FIG. 7 is a circuit diagram illustrating a variation on
Embodiment 2.
[0084] FIG. 8 is a circuit diagram illustrating a variation on
Embodiment 2.
[0085] FIG. 9 is an equivalent circuit diagram illustrating a case
where one protection switch has turned on according to Embodiment 3
of the present invention.
[0086] FIG. 10 is a circuit diagram illustrating Embodiment 4 of
the present invention.
[0087] FIG. 11 is a circuit diagram illustrating Embodiment 5 of
the present invention.
[0088] FIG. 12 is an equivalent circuit diagram of the chopper
device illustrated in FIG. 11 in a case where one switch that
performs chopper operations has short-circuited.
[0089] FIG. 13 is an equivalent circuit diagram illustrating a case
where one protection switch has turned on in the state illustrated
in FIG. 12.
[0090] FIG. 14 is a circuit diagram illustrating Embodiment 6 of
the present invention.
[0091] FIG. 15 is a circuit diagram illustrating Embodiment 7 of
the present invention.
[0092] FIG. 16 is a circuit diagram illustrating Embodiment 8 of
the present invention.
[0093] FIG. 17 is an equivalent circuit diagram of the chopper
device illustrated in FIG. 16 in a case where one switch that
performs chopper operations has short-circuited.
[0094] FIG. 18 is an equivalent circuit diagram illustrating a case
where a protection switch has turned on in the state illustrated in
FIG. 17.
[0095] FIG. 19 is a circuit diagram illustrating Embodiment 9 of
the present invention.
[0096] FIG. 20 is a circuit diagram illustrating Embodiment 10 of
the present invention.
[0097] FIG. 21 is a circuit diagram illustrating Embodiment 11 of
the present invention.
[0098] FIG. 22 is an equivalent circuit diagram illustrating a
chopper device in a case where a load has been separated in the
state illustrated in FIG. 21.
[0099] FIG. 23 is an equivalent circuit diagram illustrating a case
where a protection switch has turned on in the state illustrated in
FIG. 22.
[0100] FIG. 24 is a circuit diagram illustrating Embodiment 12 of
the present invention.
[0101] FIG. 25 is a circuit diagram illustrating Embodiment 13 of
the present invention.
[0102] FIG. 26 is a circuit diagram illustrating Embodiment 14 of
the present invention.
[0103] FIG. 27 is an equivalent circuit diagram illustrating a
chopper device in a case where a load has been separated in the
state illustrated in FIG. 26.
[0104] FIG. 28 is an equivalent circuit diagram illustrating a case
where a protection switch has turned on in the state illustrated in
FIG. 27.
[0105] FIG. 29 is a circuit diagram illustrating Embodiment 15 of
the present invention.
[0106] FIG. 30 is a circuit diagram illustrating Embodiment 16 of
the present invention.
[0107] FIG. 31 is a circuit diagram illustrating an example of a
conventional three-level chopper device.
[0108] FIG. 32 is an equivalent circuit diagram of the chopper
device illustrated in FIG. 31 in a case where one switch has
short-circuited.
[0109] FIG. 33 is an equivalent circuit diagram illustrating a
chopper device in a case where a load has been separated in the
state illustrated in FIG. 32.
DETAILED DESCRIPTION OF EMBODIMENTS
[0110] Embodiments of the present invention will be described
hereinafter with reference to the drawings. Note that in the
drawings referred to in the following embodiments, elements having
the same functions as those in FIGS. 31 to 33 will be given the
same reference numerals as the ones used in those drawings.
Embodiment 1
[0111] FIG. 1 is a circuit diagram illustrating Embodiment 1 of the
present invention. Although the primary elements of this circuit
are the same as those in FIG. 31, these elements will be described
again for the sake of clarity.
[0112] In FIG. 1, a breaker 2 constituted by a current interrupting
device having a mechanical contact, a fuse, or the like, a reactor
3, and switches 4 and 5 such as IGBTs, MOSFETs, or bipolar power
transistors, are connected in series between a positive pole and a
negative pole of a DC power source 1. A diode 6 and a capacitor 8
are connected in series to respective ends of the switch 4, and a
diode 7 and a capacitor 9 are connected in series to respective
ends of the switch 5. As such, a point of connection between the
switches 4 and 5 is connected to a point of connection between the
capacitors 8 and 9.
[0113] Meanwhile, both ends of a series circuit formed by the
capacitors 8 and 9 and a point of connection (midpoint) between the
capacitors 8 and 9 constitute output terminals of a three-level
chopper device, and a load 101 is connected between these output
terminals. The load 101 includes a series circuit of the switches
10 and 11, which are IGBTs or the like, that constitute a
half-bridge inverter, and an AC motor 12.
[0114] Note that the load 101 may include a full-bridge
single-phase or three-phase inverter, or switches, resistance
loads, and so on.
[0115] Furthermore, in Embodiment 1, protection switches 21 and 22
are connected in parallel to the switches 4 and 5, respectively.
IGBTs, MOSFETs, bipolar power transistors, or the like can be used
as these switches 21 and 22.
[0116] During normal operations in which chopper operations are
realized by the switches 4 and 5 turning on and off, the switches
21 and 22 may be kept off, or the switches 4 and 21 may be turned
on and off simultaneously while the switches 5 and 22 are turned on
and off simultaneously.
[0117] If, for example, the one switch 4 that performs the chopper
operations has short-circuited, turning the switches 10 and 11 in
the inverter in the subsequent stage off and separating the load
101, and then turning the other switch 5 that performs the chopper
operations off, will result in the equivalent circuit illustrated
in FIG. 2.
[0118] In the circuit illustrated in FIG. 2, series resonance
current produced by the reactor 3 and the capacitor 9 flows from
the DC power source 1 via the switch 4, which is conductive due to
the short-circuit fault, along a path a indicated by the broken
line. As described earlier, the series resonance current cannot be
controlled by the switch 4 due to the short-circuit fault, and thus
unless some sort of measures are taken, a voltage greater than the
breakdown voltage of the capacitor 9 will be applied thereto,
leading to a risk of the capacitor 9 being damaged by overvoltage,
exploding, or the like.
[0119] Accordingly, in the present embodiment, the equivalent
circuit illustrated in FIG. 3 is formed by tuning the protection
switch 22 on before opening the breaker 2 in cases where a
short-circuit fault is presumed to occur in the switch 4.
[0120] According to FIG. 3, current from the DC power source 1 is
short-circuited by the switch 22 and flows along a path b. The
current therefore does not flow to the capacitor 9, which makes it
possible to prevent the capacitor 9 from being damaged by
overvoltage.
[0121] During this time, the breaker 2 is on, and thus the current
flowing from the DC power source 1 to the reactor 3 increases.
However, the current in the path b can be interrupted by then
operating the breaker 2, which makes it possible to stop the
operation of the chopper device.
[0122] Here, a high-power semiconductor element may be used as the
switch 22 so that the current flowing in the path b in the circuit
state illustrated in FIG. 3 can be withstood until the interrupting
by the breaker 2 is complete, or a low-power semiconductor element
having a low short-circuit tolerance may be used as the switch 22
and the switch 22 may then be allowed to short-circuit. Even if the
switch 22 does short-circuit, that energy is vastly lower than when
the capacitor 9 is damaged by overvoltage, and thus the danger
thereof can be greatly reduced.
[0123] Even in the case where the switch 4 and the diode 6 have
short-circuited simultaneously, turning the switch 5 off results in
a series resonance circuit of the DC power source 1, the reactor 3,
and the capacitor 9 being formed. Thus the switch 22 may be turned
on to create the path b in the same manner as described above so as
to eliminate the current path a passing through the capacitor.
[0124] Aside from the above-described examples, in a case of a
short-circuit fault in the switch 5 or simultaneous short-circuit
faults of the switch 5 and the diode 7, the output-side capacitor
can be prevented from being damaged by overvoltage by turning the
switch 21 on to eliminate a current path passing through the
capacitor 8.
[0125] Accordingly, from Embodiment 2 onward, a case in which only
the switch 4 has short-circuited will be described as a
representative example. Operations for when the switch 4 and the
diode 6 have short-circuited simultaneously, for when the switch 5
has short-circuited, and for when the switch 5 and the diode 7 have
short-circuited simultaneously can be inferred easily, and thus
descriptions thereof will be omitted.
Embodiment 2
[0126] FIG. 4 is a circuit diagram illustrating Embodiment 2 of the
present invention.
[0127] The circuit configuration illustrated in FIG. 4 is
substantially the same as that illustrated in FIG. 1, but differs
from that illustrated in FIG. 1 in that: the switch 4 and the diode
6 are housed in a single package as a chopper module; the switch 5
and the diode 7 are similarly housed in a single package as a
chopper module; and furthermore, the switches 21 and 22 are housed
in mutually different packages. Note that the long-dash-short-dash
lines in FIG. 4 indicate the packages.
[0128] In the case where the protection switch 22 is turned on
after the switch 4 has short-circuited and the equivalent circuit
illustrated in FIG. 3 is then formed as a result of the
short-circuit the switches 4 and 22 have been damaged and must
therefore be replaced quickly. However, the switch 5 is not damaged
and thus does not need to be replaced.
[0129] Here, assume a case where the switches 4 and 21 and the
diode 6 are housed in a single package and the switches 5 and 22
and the diode 7 are housed in a single package, as illustrated in
FIG. 5. When a fault has occurred in the switches 4 and 22, it is
sufficient to replace only those semiconductor elements. However,
if the packages housing the switches 4 and 22 illustrated in FIG. 5
are replaced, the unaffected switches 21 and 5 housed in those
packages will also be replaced.
[0130] However, if the packaging is carried out as illustrated in
FIG. 4, the unaffected switches 21 and 5 will not be needlessly
replaced when the switches 4 and 22 are replaced.
[0131] Additionally, in the case where the switches 21 and 22 are
housed within the same package as illustrated in FIG. 6, the
switches 21 and 22 within the package housing the short-circuited
switch 22 will be replaced at the same time, but the switch 5 and
the diode 7 need not be replaced.
[0132] Furthermore, in the case where the diode 6 and the switch 21
are housed in the same package, the diode 7 and the switch 22 are
housed in the same package, and the switches 4 and 5 are housed in
mutually different packages as illustrated in FIG. 7, replacing the
switch 22, for example, means that the diode 7 will also be
replaced at the same time, but the switch 5 need not be
replaced.
[0133] Here, the switches 4 and 5 being housed in the same package
means that the switch 5 will be replaced when the switch 4 is
replaced, and this configuration is therefore not preferable from
the standpoint of reducing the number of semiconductor elements to
be replaced.
[0134] A module housing semiconductor elements for a chopper device
(switches and diodes) generally costs more than a protection
switch, which is sufficient as long as it has the necessary
breakdown voltage. Thus if, as illustrated in FIGS. 6 and 7, the
semiconductor elements for the chopper device and the protection
switches are housed in mutually different packages so as to avoid a
situation in which the semiconductor elements for the chopper
device are needlessly replaced, the cost of the device can be
reduced.
[0135] Additionally, there are cases where it is necessary to
select a package in which the switches 4 and 5 are housed in
packages along with a freewheel diode or the like that has no
direct relation to the chopper operations, as illustrated in FIG.
8. In the case where such packages are used, but modules housing
undamaged switches are not to be replaced, it is preferable that he
protection switches 21 and 22 be connected outside the packages of
the semiconductor elements that carry out chopper operations, as
illustrated in FIGS. 4, 8, and so on.
[0136] Thus even in the case where the switch 22, which was turned
on when the arm housing the switch 4 short-circuited, has itself
short-circuited, it is sufficient to replace the package housing
the switch 22, and the package housing the switch 5 need not be
replaced. It goes without saying that it is necessary to replace
the package housing the switch 4.
Embodiment 3
[0137] Embodiment 3 of the present invention will be described
next. The circuit configuration according to Embodiment 3 is the
same as that illustrated in FIG. 4, and thus the following
descriptions will be given with reference to FIG. 4.
[0138] As in FIG. 4, in Embodiment 3, the switch 4 and the diode 6
are housed in a single package as a chopper module, the switch 5
and the diode 7 are housed in a single package as a chopper module,
and the protection switches 21 and 22 are housed in mutually
different packages. A further feature of Embodiment 3 is that
diodes constituted by wide band-gap semiconductors, such as silicon
carbide Schottky barrier diodes (SiC-SBDs), are used as the diodes
6 and 7, and elements made of a silicon semiconductor are used as
the protection switches 21 and 22 connected outside the chopper
modules.
[0139] The switches 21 and 22 are not conductive during normal
operations of the chopper device and it is therefore not necessary
to be concerned with loss or the like. Accordingly, it is not
necessary to use elements constituted by low-loss and high-cost
wide band-gap semiconductors. Rather, it is sufficient to use
low-cost elements made of a silicon semiconductor.
[0140] Even in the case where the switch 22 turns on in response to
a short-circuit fault in the switch 4 as illustrated in FIG. 9 and
the switch 22 has short-circuited thereafter as a result, the
chopper module housing the diode 7 made of a wide band-gap
semiconductor is undamaged and thus need not be replaced.
[0141] Thus if low-cost elements made of silicon are used as the
protection switches 21 and 22 in this manner, a situation in which
the chopper module housing the high-cost diode 7 is unnecessarily
replaced can be avoided.
Embodiment 4
[0142] FIG. 10 is a circuit diagram illustrating Embodiment 4 of
the present invention.
[0143] Although the circuit configuration according to the present
embodiment is substantially the same as that illustrated in FIGS. 4
and 8, a feature of the present embodiment is that elements
constituted by wide band-gap semiconductors such as silicon carbide
MOS field effect transistors (SiC-MOSFETs) are used as the switches
4 and 5 that carry out chopper operations, and elements made of
silicon are used as the protection switches 21 and 22. As described
earlier, the long-dash-short-dash lines in the drawings indicate
the packages housing the respective components.
[0144] According to Embodiment 4, even in the case where, for
example, the switch 22 is turned on in response to a short-circuit
fault in the switch 4 and the switch 22 has short-circuited
thereafter as a result, the chopper module housing the switch 5
made of a wide band-gap semiconductor has not faulted and thus need
not be replaced. Thus compared to the example illustrated in FIG.
5, a situation in which the chopper module is needlessly replaced
can be avoided.
Embodiment 5
[0145] FIG. 11 is a circuit diagram illustrating Embodiment 5 of
the present invention.
[0146] In Embodiment 5, protection switches 23 and 24 are connected
in parallel to the capacitors 8 and 9, respectively.
[0147] If, when the one switch 4 that performs chopper operations
has short-circuited, the load 101 is separated and the other switch
5 turns off, the equivalent circuit illustrated in FIG. 12 is
formed. In the circuit illustrated in FIG. 12, series resonance
current flows from the DC power source 1 via the switch 4, which is
in a short-circuited state, along the path a including the reactor
3 and the capacitor 9. Even in this case, the switch 4 cannot
control the series resonance current due to the fault, and there is
thus a risk that the capacitor 9 will be damaged by
overvoltage.
[0148] However, if a short-circuit fault is presumed to arise in
the switch 4, and the switch 24 is then turned on before the
breaker 2 is opened, the circuit illustrated in FIG. 12 will become
the equivalent circuit illustrated in FIG. 13. Accordingly, the
series resonance current from the DC power source 1 will flow along
a path c, and will not flow to the capacitor 9, which makes it
possible to prevent the capacitor 9 from being damaged by
overvoltage.
[0149] In the present embodiment, the switch 23 and the capacitor 8
may be housed in a single package, and the switch 24 and the
capacitor 9 may be housed in a single package. Alternatively, these
components may be housed in mutually different packages.
Furthermore, the switches 23 and 24 may be housed in the same
package, or may be housed in mutually different packages.
Embodiment 6
[0150] FIG. 14 is a circuit diagram illustrating Embodiment 6 of
the present invention.
[0151] According to the present embodiment, a chopper module in
which the switch 4 and the diode 6 are housed in the same package,
a chopper module in which the switch 5 and the diode 7 are housed
in the same package, and packages that individually house the
switches 23 and 24 respectively, are used in the configuration
illustrated in FIG. 11. Additionally, elements made of wide
band-gap semiconductors such as SiC-SBDs are used as the diodes 6
and 7, whereas elements made of silicon semiconductor are used as
the protection switches 23 and 24 and are connected outside the
chopper modules.
[0152] According to Embodiment 6 too, low-cost elements made of
silicon semiconductor can be used as the switches 23 and 24 that
are not conductive during normal operations of the chopper
device.
[0153] Additionally, if, when a short-circuit fault is presumed to
arise in the switch 4, the switch 24 is turned on before the
breaker 2 is opened, current from the DC power source 1 flows along
the path c and thus does not flow to the capacitor 9, as
illustrated in FIG. 13. Accordingly, the capacitor 9 is prevented
from being damaged by overvoltage. Even if the switch 24 does
short-circuit, the chopper module housing the diode 7 made of a
wide band-gap semiconductor is not damaged. This makes it possible
to avoid a situation where the module is needlessly replaced.
Embodiment 7
[0154] FIG. 15 is a circuit diagram illustrating Embodiment 7 of
the present invention.
[0155] According to the present embodiment, elements made of wide
band-gap semiconductors such as SiC-MOSFETs are used as the
switches 4 and 5 in FIG. 14, whereas elements made of silicon
semiconductor are used as the protection switches 23 and 24 and are
connected outside the chopper modules.
[0156] According to the present embodiment too, the capacitor 9 can
be prevented from being damaged by overvoltage when the switch 4
short-circuits, and a situation in which the chopper module housing
the switch 5 made of a wide band-gap semiconductor is needlessly
replaced can be avoided, in the same manner as in Embodiment 6.
Embodiment 8
[0157] FIG. 16 is a circuit diagram illustrating Embodiment 8 of
the present invention.
[0158] In Embodiment 8, a protection switch 25 is connected between
an anode of the diode 6 and a cathode of the diode 7, in place of
the protection switches 21 and 22 illustrated in FIG. 1.
[0159] In the case where there is a period, during operation of the
chopper device, where the switches 4 and 5 are turned on
simultaneously, the switch 25 may also be turned on at the same
time.
[0160] If the load 101 is separated at the time of a short-circuit
fault in the switch 4, the equivalent circuit illustrated in FIG.
16 will become that illustrated in FIG. 17. In this case too,
uncontrollable series resonance current will flow, via the switch 4
that is conductive, from the DC power source 1 in the path a
passing through the capacitor 9, and there is thus a risk that the
capacitor 9 will be damaged by overvoltage.
[0161] Accordingly, if, in the case where a short-circuit fault is
presumed to arise in the switch 4, the protection switch 25 is
turned on before the breaker 2 is opened, the current from the DC
power source 1 will flow in a path d, as illustrated in FIG. 18,
and thus will not flow to the capacitor 9. The capacitor 9 is thus
prevented from being damaged by overvoltage.
Embodiment 9
[0162] FIG. 19 is a circuit diagram illustrating Embodiment 9 of
the present invention.
[0163] According to the present embodiment, a chopper module in
which the switch 4 and the diode 6 are housed in the same package,
a chopper module in which the switch 5 and the diode 7 are housed
in the same package, and a package that houses only the switch 25,
are used in the configuration illustrated in FIG. 16.
[0164] Additionally, elements made of wide band-gap semiconductors
such as SiC-SBDs are used as the diodes 6 and 7, and an element
made of silicon semiconductor is used as the switch 25.
[0165] According to the present embodiment too, the capacitor 9 can
be prevented from being damaged by overvoltage when a short-circuit
fault arises in the switch 4, in the same manner as in Embodiment
8.
[0166] Additionally, the switch 25 and the switch 5 are housed in
different packages. As such, even in the case where the switch 25
turns on in response to a short-circuit fault in the switch 4 and
the switch 25 has short-circuited thereafter as a result, a
situation in which the chopper module housing the diode 7 made of a
high-cost wide band-gap semiconductor is needlessly replaced can be
avoided.
Embodiment 10
[0167] FIG. 20 is a circuit diagram illustrating Embodiment 10 of
the present invention.
[0168] According to the present embodiment, elements made of wide
band-gap semiconductors such as SiC-MOSFETs are used as the
switches 4 and 5 in FIG. 19, whereas an element made of silicon
semiconductor is used as the protection switch 25.
[0169] According to the present embodiment too, the capacitor 9 can
be prevented from being damaged by overvoltage when a short-circuit
fault arises in the switch 4, and the switch 25 can also be
replaced independently. As such, a situation in which the chopper
module housing the switch 5 made of a wide band-gap semiconductor
is needlessly replaced can be avoided, in the same manner as in
Embodiment 9.
Embodiment 11
[0170] FIG. 21 is a circuit diagram illustrating Embodiment 11 of
the present invention.
[0171] In the present embodiment, a protection switch is added to a
normal two-level boosting chopper device.
[0172] In FIG. 21, 102 indicates a load including a full-bridge
inverter constituted by switches 10a, 10b, 11a, and 11b, and a
motor 12. A series circuit constituted by a diode 6 and a switch
28, and a capacitor 26, are connected in parallel to a DC input
side of the stated inverter. Meanwhile, a protection switch 27 is
connected in parallel to the switch 28. Other configurations are
the same as in the embodiments described above.
[0173] The switch 28 is an element for performing chopper
operations, and the switch 27 may also be turned at the same time
as the switch 28 is turned on.
[0174] In the present embodiment, in the case where there is an
indication that, for example, the switches 10a, 10b, 11a, and 11b
or the like in the inverter will fault and cause overvoltage in the
capacitor 26, the equivalent circuit illustrated in FIG. 22 is
formed by separating the load 102 and turning the switch 28 that
performs chopper operations off.
[0175] In the circuit illustrated in FIG. 22, until the breaker 2
is opened, the reactor 3 and the capacitor 26 are connected in
series to the respective ends of the DC power source 1, thus
forming a series resonance circuit. As such, current flowing along
a path e will cause the voltage of the capacitor 26 to rise beyond
the voltage thereof during normal operations.
[0176] As described above, with a three-level boosting chopper
device such as those described in Embodiments 1 to 10, there are
cases where the device is operated with the voltage of the
output-side capacitor set lower than the voltage of the DC power
source 1. However, if a series resonance circuit is formed by the
reactor and the capacitor in such a state, the voltage of the
capacitor may increase greatly.
[0177] As opposed to this, according to the two-level boosting
chopper device illustrated in FIG. 21, the device is normally
operated with the voltage of the output-side capacitor 26 set
higher than the voltage of the DC power source 1. As such, even if
a series resonance circuit such as that illustrated in FIG. 22 is
formed, it is difficult to conceive of the voltage of the capacitor
26 greatly rising beyond the voltage thereof during normal
operations. However, with a chopper device for use in railways, in
the case where a DC power source voltage fluctuates drastically due
to bounce or the like the voltage of the DC power source 1 rises
suddenly immediately before the switch 28 is turned off, there is a
risk that the voltage reaching the capacitor 26 will become
extremely high.
[0178] Even at such a time, in the case where an indication that
the capacitor 26 will enter a state of overvoltage is detected,
turning the protection switch 27 on before the breaker 2 is opened
results in the equivalent circuit illustrated in FIG. 23 being
formed. As a result, current from the DC power source 1 flows along
the path d, and the path e indicated in FIG. 22 is eliminated. This
makes it possible to prevent the capacitor 26 from being damaged by
overvoltage, the switch 28 breaking down or being damaged by
overvoltage, and so on. After the switch 27 has been turned on, the
chopper device operations are stopped by operating the breaker 2 to
interrupt the current from the DC power source 1.
[0179] Although the switches 27 and 28 may be housed in the same
package, it is desirable that these switches be housed in mutually
different packages.
[0180] The protection switch 27 need not be conductive during
normal operations of the chopper, and thus it is not necessary to
use a high-performance, high-cost semiconductor element. For
example, a low-cost element made of silicon semiconductor can be
used. Accordingly, in the case where high-cost elements such as
wide band-gap semiconductors are used as the switch 28, the diode
6, and so on, replacing only the low-cost switch 27 improves the
cost performance.
Embodiment 12
[0181] FIG. 24 is a circuit diagram illustrating Embodiment 12 of
the present invention.
[0182] According to the present embodiment, a SiC-SBD made of a
wide band-gap semiconductor is used as the diode 6 in the chopper
module. Additionally, the diode 6 and the switch 28 are housed in
the same package, and the protection switch 27 is housed in a
different package. A low-cost element made of silicon semiconductor
is used as the switch 27.
[0183] Having the switches 27 and 28 housed in mutually different
packages as in the present embodiment means that even if the
protection switch 27 has short-circuited after being turned on, it
is possible to change only the switch 27.
[0184] If the voltage of the capacitor 26 rises and the switch 28
is damaged by overvoltage, the diode 6 housed in the same package
as the switch 28, or in other words, the diode 6 made of a
high-cost wide band-gap semiconductor, also needs to be
replaced.
[0185] According to the present embodiment, only the switch 27 is
housed in a different package, and thus turning the switch 27 on
before the switch 28 is damaged by overvoltage makes it possible to
protect the capacitor 26, the switch 28, the diode 6, and so on.
Additionally, even in the case where the switch 27 has
short-circuited thereafter, it is only necessary to replace the
low-cost switch 27.
Embodiment 13
[0186] FIG. 25 is a circuit diagram illustrating Embodiment 13 of
the present invention.
[0187] According to the present embodiment, a SiC-MOSFET or the
like made of a wide band-gap semiconductor is used as the switch 28
described in Embodiment 11. An element made of silicon
semiconductor is used as the protection switch 27.
[0188] Operations according to the present embodiment are basically
the same as in the above-described Embodiment 11 and Embodiment 12,
and thus details thereof will be omitted. However, if the switch 27
is turned on before the switch 28 is damaged by overvoltage due to
the voltage of the capacitor 26, the capacitor 26, the high-cost
switch 28, and so on can be protected.
[0189] Additionally, housing the switches 27 and 28 in mutually
different packages means that even if the switch 27 has then
short-circuited, it is possible to replace only the low-cost switch
27, which provides high cost performance.
Embodiment 14
[0190] FIG. 26 is a circuit diagram illustrating Embodiment 14 of
the present invention.
[0191] According to the present embodiment, a protection switch 29
is connected in parallel to the capacitor 26 as illustrated in FIG.
26, in place of the protection switch 27 described in Embodiment 11
with reference to FIG. 21.
[0192] In the case where the inverter or the like of the load 102
has faulted, separating the load 102 and turning the switch 28 that
performs chopper operations off will result in the equivalent
circuit illustrated in FIG. 27 being formed. In the case where an
indication that the capacitor 26 will enter a state of overvoltage
is detected, if the protection switch 29 is turned on before the
breaker 2 is opened, current in the path e indicated in FIG. 27
flows in a path f indicated in FIG. 28, and no longer flows to the
capacitor 26. As a result, the capacitor 26 can be prevented from
being damaged by overvoltage, and the switch 28 can be prevented
from breaking down or being damaged by overvoltage.
[0193] After this, the chopper device operations are stopped by
operating the breaker 2 to interrupt the current from the DC power
source 1.
[0194] Although the switches 28 and 29 may be housed in the same
package, housing these switches in mutually different packages
means that in the case where, for example, the switch 29 has
short-circuited and thus needs to be replaced, it is only necessary
to replace the switch 29.
[0195] Accordingly, even in the case where a low-cost element made
of silicon semiconductor is used as the switch 29, which need not
be conductive during normal operations of the chopper device, and
high-performance and high-cost semiconductor elements are used as
the switch 28, the diode 6, and so on that perform chopper
operations, it is not necessary to replace the switch 28, which is
economical.
Embodiment 15
[0196] FIG. 29 is a circuit diagram illustrating Embodiment 15 of
the present invention.
[0197] According to the present embodiment, an element made of a
wide band-gap semiconductor such as a SiC-SBD is used as the diode
6 illustrated in FIG. 26. Additionally, a chopper module
constituted by the diode 6 and the switch 28 is housed in the same
package, whereas the switch 29 is housed in a different
package.
[0198] In the present embodiment too, when a fault has occurred in
the inverter, for example, the capacitor 26 can be prevented from
being damaged by overvoltage by turning the switch 29 on and
causing current to flow in the path f indicated in FIG. 28.
Meanwhile, in the case where the switch 29 short-circuits
thereafter and therefore must be replaced, it is possible to
replace only the switch 29. As such, the chopper module including
the high-cost diode 6 can continue to be used.
Embodiment 16
[0199] FIG. 30 is a circuit diagram illustrating Embodiment 16 of
the present invention.
[0200] According to the present embodiment, an element made of a
wide band-gap semiconductor such as a SiC-MOSFET is used as the
chopper switch 28 illustrated in FIG. 26, and a low-cost element
made of silicon semiconductor is used as the protection switch
29.
[0201] With the present embodiment too, the capacitor 26 can be
prevented from being damaged by overvoltage according to the same
principles as those described in Embodiment 14 and Embodiment 15.
Additionally, in the case where the switch 29 that has been turned
on then short-circuits and must be replaced, it is sufficient to
replace only the switch 29, and the chopper module including the
high-cost switch 28 can continue to be used.
[0202] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention
without departing from the spirit or scope of the invention. Thus,
it is intended that the present invention cover modifications and
variations that come within the scope of the appended claims and
their equivalents. In particular, it is explicitly contemplated
that any part or whole of any two or more of the embodiments and
their modifications described above can be combined and regarded
within the scope of the present invention.
* * * * *